Graphene is a single atomic layer of graphite, and currently holds interest for many electronic and spintronic device applications due to graphene's electronic properties, including high mobility, high saturation velocity, stable crystal structure, and ultrathin layer thickness. To be utilized in electronic and spintronic device applications, graphene must rest on an electronically semiconducting or insulating substrate.
Current methods of producing graphene involve either growing graphene on a transition metal substrate and then transferring a single graphene sheet onto an insulating substrate, or growing graphene by thermal evaporation of silicon from bulk SiC(0001) substrates.
In the first method, the graphene growth on the transition metal substrate is typically performed by thermal decomposition of a hydrocarbon precursor, or by formation of highly oriented pyrolitic graphite (a commercial substance), followed by chemical or manual exfoliation of a single graphene sheet and manual placement on an insulating substrate, such as SiO2. These methods tend to be unpractical for large-scale production of electronic devices with consistent electronic properties, including graphene-substrate contact characteristics.
In the second method, the graphene remains on the semiconducting SiC substrate after the thermal of evaporation of the silicon from the SiC substrate. The transfer of graphene sheets grown by this second method is not practical. In addition, the growth process occurs at temperatures greater than 1500 K and does not allow for growth or integration with any device materials other than SiC—a material with numerous processing problems for device manufacture.
Recently, boron nitride (BN) has become of interest for its insulating characteristics and potential for use in nanotechnology. Hexagonal phase BN films may be grown by atomic layer deposition using layer-by-layer deposition of precursors to give a film thickness controllable to atomic dimensions. Ordered hexagonal (BN111) films 1 atomic layer thick have been grown on Ni(111), Cu(111) and Rh(111) or Ru(0001) surfaces by thermal decomposition of borazinc. However, growth of multilayer films by current methods is inhibited because the first BN monolayer renders the surface chemically inert. Moreover, the chemical structure of monolayer films grown by borazine decomposition on certain substrates such as Ru(0001) and Rh(111) is highly puckered—a “nanomesh”—and may be unsuitable for subsequent growth of ordered films. In addition, although certain monolayer (BN111) and graphene/monolayer (BN111) films have been grown, the electronic properties of these graphene films are greatly affected by electronic interaction through the single atomic layer of the graphene to the substrate. Thus, research continues to be conducted to provide useful graphene structures for device applications.